A British company claims a revolutionary breakthrough in engine technology that blurs the lines between air and space travel — bringing any destination on Earth within a four-hour trip.

Reaction Engines’ Sabre, an engine that functions as a jet in the air and a rocket in space, would power a reusable space-plane that routinely flies into orbit.

The Sabre just won the stamp of approval from the European Space Agency, reports Reuters:

“ESA are satisfied that the tests demonstrate the technology required for the Sabre engine development,” the agency’s head of propulsion engineering Mark Ford told a news conference. “One of the major obstacles to a re-usable vehicle has been removed,” he said. “The gateway is now open to move beyond the jet age.”

The company’s space-plane, the Skylon, is still on the drawing board. But Reaction has achieved a key breakthrough in air-cooling technology, solving a problem that previously would have melted a jet engine seeking to exceed 2.5 times the speed of sound. This means the Sabre-powered Skylon, unlike a traditional rocket-launched spaceship, could draw oxygen from the air, eliminating the need for massive tanks of liquid oxygen contained in single-use rockets.

This approach enables SABRE-powered vehicles to save carrying over 250 tons of on-board oxidant on their way to orbit, and removes the necessity for massive throw-away first stages that are jettisoned once the oxidant they contain has been used up, allowing the development of the first fully re-usable space access vehicles such as SKYLON.

While this sounds simple, the problem is that in air-breathing mode, the air must be compressed to around 140 atmospheres before injection into the combustion chambers which raises its temperature so high that it would melt any known material. SABRE avoids this by first cooling the air using a Pre-cooler heat exchanger until it is almost a liquid. Then a relatively conventional turbo compressor using jet engine technology can be used to compress the air to the required pressure.